Magnetic levitation conveyor apparatus

ABSTRACT

A magnetic levitation conveyor apparatus has levitation electromagnets, linear motors, and displacement sensors which are disposed outside of a tunnel, and a carriage of simple structure which is movable in the tunnel. The carriage is of canned structure for preventing gases from being generated. The carriage of canned structure allows the tunnel to have a reduced cross-sectional area and to be filled with a highly purified atmosphere such as of a high vacuum. The tunnel has substantially orthogonal branches at a branched point. In the branched point, the carriage can move, while being lifted out of contact with the tunnel partition, with a directional change from a main conveyor passage into a branched conveyor passage. The magnetic levitation conveyor apparatus is highly practical as it can control the carriage to be lifted and moved as described above.

TECHNICAL FIELD

The present invention relates to a magnetic levitation conveyorapparatus, and more particularly to a magnetic levitation conveyorapparatus having a carriage for carrying a workpiece such as a wafer orthe like in a tunnel that is kept in a highly clean atmosphere such as avacuum or the like, the carriage being magnetically levitated formovement out of contact with a partition.

BACKGROUND ART

There have been growing demands in the process of semiconductorfabrication for transferring and receiving a wafer between variousprocessing steps entirely in a clean space. Since semiconductor productstend to become easily defective when contaminated by impurities, theyshould preferably be conveyed in a clean room which is highly purified.As semiconductors are processed to smaller dimensions, the diameter ofparticles which cause problems is smaller. Therefore, it is difficult toproduce desirable purified spaces in conventional clean rooms. It hasbeen considered to convey a wafer or the like in a vacuum whereparticles are not suspended in the space because of less Brownianmotion. Specifically, there has heretofore been proposed a magneticlevitation conveyor apparatus having a carriage for carrying a workpiecesuch as a wafer or the like in a vacuum maintained in a tunnel, thecarriage being magnetically levitated for movement out of contact with apartition.

There has also been proposed a magnetic levitation conveyor apparatushaving a carriage movable out of contact with a partition of a tunnelwhich is filled with a clean nitrogen gas or the like, rather than avacuum.

For example, Japanese laid-open patent publications Nos. 61-295926 and1-299119 disclose magnetic levitation vacuum conveyor apparatus in whicha carriage that is magnetically levitated is movable along a conveyorpassage in a partition maintained in a highly purified vacuumenvironment. Japanese laid-open patent publication No. 63-194502 andJapanese laid-open utility model publication No. 1-134998 disclosemagnetic levitation vacuum conveyor apparatus of the type in whichmembers that possibly produce dirt and dust particles are housed in thetunnel, i.e., levitating electromagnets, displacement sensors, andlinear motors which are arrayed in a conveyor passage are housed in thetunnel (can), and a carriage is movable in a vacuum (purifiedatmosphere) outside of the tunnel (can).

Japanese laid-open patent publications Nos. 53-34272, 61-277303,4-75404, and Japanese laid-open utility model publication No. 59-146326disclose magnetic levitation conveyor apparatus having a carriage(movable body) suspended under magnetic attractive forces produced bylevitating electromagnets arrayed along a conveyor passage for movementwhile being levitated off the conveyor passage.

In the magnetic levitation conveyor apparatus in which the carriage in avacuum tunnel (partition) is movable while being suspended by levitatingelectromagnets disposed outside of the partition as disclosed inJapanese laid-open patent publication No. 61-295926, however, it isnecessary to install a permanent magnet on the carriage, and thepartition is required to be of a complex cross-sectional shape. Sincevarious parts of the carriage and the partition itself discharge variousgases and produce fine particles, it has been difficult to create a highdegree of vacuum, and the workpiece carried by the carriage tends to becontaminated.

In the case where a purified space is produced by passing a nitrogen gasin a tunnel, it has been customary to place levitating electromagnets,linear motors, etc. in the tunnel. However, inasmuch particles depositedin gaps between electromagnet coils cannot fully be removed, theseparticles are discharged into the tunnel. Because the electromagnets aredisposed in the tunnel, it has been quite laborsome to replace any ofthe electromagnet coils which is broken.

In the magnetic levitation vacuum conveyor apparatus of the type inwhich members that possibly produce dirt and dust particles are housedin the tunnel, cables for supplying a control current to the levitatingelectromagnets, the displacement sensors, or the linear motors in thetunnel (can) are exposed in a highly purified atmosphere such as avacuum. Such an arrangement poses a problem on the handling of thecables, and the maintenance of components in the tunnel (can).

The present invention has been made in view of the above drawbacks. Itis an object of the present invention to provide a magnetic levitationconveyor apparatus which has levitating electromagnets, linear motors,displacement sensors, etc. that are disposed outside of a tunnel, and acarriage movable in the tunnel, the carriage being of a simplestructure, i.e., a canned structure, for preventing gases from beingproduced, the tunnel having a reduced cross section for being highlypurified therein, and the carriage being well controllable to belevitated and moved in the tunnel.

The process of semiconductor fabrication employs a variety of processingapparatus for carrying out lithography, growing various films, anddiffusing materials. These processing apparatus have to beinterconnected by tunnels in which semiconductor wafers or the like needto be conveyed through a highly purified (high vacuum) atmosphere.

Accordingly, it is another object of the present invention to provide apractical magnetic levitation conveyor apparatus including a tunnelwhich has a branch, and a carriage that can be levitated in the tunneland moved from a main conveyor passage into a branched conveyor passageat the branched point while being held out of contact with a partitionof the tunnel.

DISCLOSURE OF THE INVENTION

A first aspect of the present invention is concerned with a tunnelstructure in a magnetic levitation conveyor apparatus having a tunneldefined by a partition, a carriage disposed in said tunnel, a pluralityof levitation electromagnets for lifting the carriage out of thepartition, linear motors for moving the carriage, and displacementsensors for detecting a vertical distance up to said carriage,characterized in that said levitation electromagnets, said linearmotors, and said displacement sensors are disposed outside of saidpartition, and housed in respective thin-wall casings extending throughsaid partition and partly exposed in said tunnel.

A second aspect of the present invention is concerned with the structureof a conveyor passage and a carriage in a magnetic levitation conveyorapparatus comprising a tunnel defined by a partition and havingsubstantially orthogonal branched passages, a carriage movable in alevitated state through said tunnel for conveying a workpiece,levitation electromagnets having at least two rows of magnetic polesdisposed on an upper portion of said partition for lifting the carriageout of contact with the partition, electromagnets serving as linearmotors and having at least one row of magnetic poles disposed on saidpartition for moving said carriage out of contact with the partition, atleast two rows of displacement sensors disposed on said partition fordetecting a levitated position of said carriage, and control circuitsfor controlling exciting currents supplied to said levitationelectromagnets based on output signals from said displacement sensors,said carriage having, on an upper surface thereof, two parallel magneticelements corresponding to said two rows of magnetic poles of thelevitation electromagnets and two parallel magnetic elementsperpendicular to the first-mentioned two parallel magnetic elements, andalso having, on a lower surface thereof, an electrically conductivemember corresponding to the magnetic poles of the electromagnets servingas the linear motors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 3 show a magnetic levitation conveyor apparatusaccording to a first embodiment of the present invention. FIG. 1 is across-sectional view of the structure of a tunnel; FIG. 2 is an enlargedcross-sectional view showing the relation between a levitatingelectromagnet and a thin-wall cap; and FIG. 3 is an enlargedcross-sectional view showing the relation between a displacement sensorand a thin-wall cap.

FIGS. 4 through 6 show a magnetic levitation conveyor apparatusaccording to a second embodiment of the present invention. FIG. 4 is aset of cross-sectional views of the structures of a tunnel; FIG. 5 is aplan view of FIG. 4; and FIG. 6 is an enlarged fragmentarycross-sectional view of FIG. 5.

FIGS. 7 through 16 show a magnetic levitation conveyor apparatusaccording to a third embodiment of the present invention. FIG. 7 is asectional front elevational view of the structure of a conveyor passageand a carriage; FIG. 8 is an enlarged partial front elevational viewillustrative of the relative positional relation between a plate member20 of magnetic material and magnetic poles of a levitating electromagnet4; FIG. 9 is a perspective view of the carriage used in the conveyorapparatus shown in FIGS. 7 and 8; FIG. 10 is a view showing the layoutof magnetic pole surfaces of levitating electromagnets at a branchedpoint of a tunnel which has a substantially orthogonal branch; FIG. 11is illustrative of the structure of a magnetic member fixed to an uppersurface of the carriage, (A) being a plan view showing the relationbetween the magnetic member and magnetic pole surfaces of levitatingelectromagnets, (B) being a side elevational view showing the relationbetween the magnetic member and magnetic pole surfaces of levitatingelectromagnets, and (C) being a perspective view of the magnetic member;FIG. 12 is illustrative of the structure of the magnetic member fixed tothe upper surface of the carriage, (A) being a plan view showing therelation between the magnetic member and magnetic pole surfaces oflevitating electromagnets, (B) being a side elevational view showing therelation between the magnetic member and magnetic pole surfaces oflevitating electromagnets, and (C) being an enlarged partial view of(B); FIG. 13 is illustrative of the structure of a grooved magneticmember, (A) being a plan view showing the shape of the magnetic member,(B) being a side elevational view showing the positional relationbetween the magnetic member and C-shaped magnetic poles of levitatingelectromagnets, and (C) being an enlarged view of (B); and FIGS. 14, 15,and 16 are perspective views of various configurations of magneticmembers fixed to the upper surface of the carriage in this embodiment.

FIGS. 17 through 24 show a magnetic levitation conveyor apparatusaccording to a sixth embodiment of the present invention. FIG. 17 is aplan view of the structure of a conveyor passage at a branched point,showing a condition prior to switching directions of movement; FIG. 18is an elevational view of the conveyor passage shown in FIG. 17; FIG. 19is an enlarged partial perspective view of FIG. 17, showing a conditionin which a carriage moves in a main conveyor passage; FIG. 20 is anenlarged partial perspective view of FIG. 17, showing a condition inwhich the carriage is positioned in a branched point; FIG. 21 is a blockdiagram of a control system; FIG. 22 is a set of views showing aprocedure for switching operative/inoperative magnetic poles oflevitating electromagnets; and FIGS. 23 and 24(A), 24(B) are diagramsshowing the manner in which the gain of the levitating electromagnets iscontrolled, the horizontal axis representing the magnetic pole switchingtime and the vertical axis representing the value of gain.

FIGS. 25 through 30 show a magnetic levitation conveyor apparatusaccording to a seventh embodiment of the present invention. FIG. 25 is across-sectional view along a conveyor passage; FIG. 26 is a blockdiagram of a control system of the magnetic levitation conveyorapparatus; FIG. 27 is a diagram illustrative of a sequence of switchingconventional levitation magnetic poles; FIG. 28 is a set of diagramsillustrative of switching of the conventional magnetic poles; FIG. 29 isa diagram illustrative of switching of magnetic poles according to thepresent invention; and FIG. 30 is a set of diagrams illustrative ofswitching of magnetic poles according to another arrangement of thepresent invention.

FIGS. 31 through 33 show a magnetic levitation conveyor apparatusaccording to an eighth embodiment of the present invention. FIG. 31 is ablock diagram of a control system; FIG. 32 is a diagram showingtime-depending characteristics of an offset voltage at the time acarriage is landed; and FIG. 33 is a diagram showing time-dependingcharacteristics of an offset voltage at the time the carriage islevitated.

FIGS. 34 shows a magnetic levitation conveyor apparatus according to aninth embodiment of the present invention, i.e., is a partial sectionalside elevational view of a levitating electromagnet with a passivedamper.

FIGS. 35 and 36 show a magnetic levitation conveyor apparatus accordingto a tenth embodiment of the present invention. FIG. 35 is across-sectional view of the structure of a conveyor passage and acarriage; and FIG. 36 is a plan view of the structure of the conveyorpassage and the carriage.

FIGS. 37 and 38 show a magnetic levitation conveyor apparatus accordingto an eleventh embodiment of the present invention. FIG. 37 is across-sectional view of a conveyor passage structure having a verticalconveyor passage; and FIG. 38 is a view illustrating in detail thestructure of a table and a carriage.

FIGS. 39 through 41 show a magnetic levitation conveyor apparatusaccording to a twelfth embodiment of the present invention. FIG. 39 is aview showing a connection between a tunnel and a processing apparatus;FIG. 40 is a view showing a connection between a tunnel and a processingapparatus according to another arrangement; and FIG. 41 is a viewshowing a connection between a tunnel and a processing apparatusaccording to a conventional arrangement.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail with reference to theaccompanying drawings. In embodiments described below, the interiorspace of a tunnel is kept in a vacuum condition. However, the presentinvention is also applicable to an arrangement in which a clean gas suchas a nitrogen (N₂) gas or the like is flowed in a tunnel to create apurified space isolated from the exterior.

(1st embodiment)

A magnetic levitation conveyor apparatus according to a first embodimentof the present invention will be described below with reference to FIGS.1 through 3. As shown in FIG. 1, the magnetic levitation conveyorapparatus has a tunnel 1 constructed of a partition 2 and a carriage 3disposed in the tunnel 1. Levitating electromagnets 4 are disposedupwardly of the tunnel 1 for levitating and supporting the carriage 3out of contact with the partition 2. The levitating electromagnets 4 arepositioned on the atmospheric side, and housed respectively in thin-wallcaps 5 which serve as housing members in the form of thin-wall casings.The thin-wall caps 5 extend through the partition 2 and have respectivebottoms exposed in the tunnel 1.

FIG. 2 shows in detail the levitating electromagnet 4 (the coil isomitted from illustration) and the thin-wall cap 5. The thin-wall cap 5has a flange 5a on its upper portion, and the flange 5a is fixed to thepartition 2 by bolts 10 with an O-ring 11 interposed between the flange5a and the partition 2 for sealing the vacuum condition in the tunnel 1.The thin-wall cap 5 has a thin bottom wall 5b having a thickness t=1-2mm so as not to impede magnetic forces of the levitating electromagnet4. The thin-wall cap 5 is made of a nonmetallic material such asceramics or a metallic material which is paramagnetic and has largerelectric resistance than aluminum, e.g., stainless steel (SUS304).

Electromagnet 6 of linear motors for moving the carriage 3 are disposeddownwardly of the tunnel 1. Each of the electromagnets 6 is positionedon the atmospheric side, and housed in a thin-wall cap 7 which serves asa housing member in the form of a thin-wall casing. The thin-wall cap 7extends through the partition 2 and has a bottom exposed in thetunnel 1. The thin-wall cap 7 is made of a nonmetallic material such asceramics or a metallic material which is paramagnetic and has largerelectric resistance than aluminum, e.g., stainless steel (SUS304).

Displacement sensors 8 are disposed on left and right sides of thebottom of the tunnel 1. The displacement sensors 8 are housed inrespective thin-wall caps 9 in the form of thin-wall casings whichextend through the partition 2 and have tops exposed in the tunnel 1.Each of the displacement sensors 8 comprises an eddy-current sensor, andeach of the thin-wall caps 9 is made of ceramics for not impeding thesensing action of the eddy-current sensor. FIG. 3 shows in detail thedisplacement sensor 8 and the thin-wall cap 9. The thin-wall cap 9 has aflange 9a, and an O-ring 11 is interposed between the flange 9a and thepartition 2 for sealing the vacuum condition in the tunnel 1. Thethin-wall cap 9 has a thin top wall 9b having a thickness t=1-2 mm, sothat the distance between the displacement sensor 8 and the carriage 3falls in a sensing range of the displacement sensor 8.

Although not shown, the levitating electromagnets 4, the electromagnet6, and the displacement sensors 8 are arranged at equal intervals in thedirection in which the carriage 3 is movable forward (the directionnormal to the sheet of FIG. 1). An electromagnet (not shown) of anelectromagnetic brake is disposed in a position where the carriage 3 isto stop.

In the magnetic levitation conveyor apparatus of the above structure,the displacement sensors 8 detect the vertical distance from thedisplacement sensors 8 to the carriage 3, and outputs the detecteddistance to a levitation control circuit (not shown). In response to theoutput signal from the displacement sensors 8, the levitation controlcircuit increases or reduces an exciting current supplied to thelevitating electromagnets 4 to control magnetic attractive forces actingon the carriage 3. Accordingly, the carriage 3 can stably be levitatedvertically out of contact with the partition 2. The electromagnets 6 ofthe linear motors generate an eddy current in an electrically conductivemember (not shown) on the lower surface of the carriage 3 for propellingand moving the carriage 3 in the forward direction (the direction normalto the sheet of FIG. 1).

In this embodiment, the levitating electromagnets 4, the linear motors6, and the displacement sensors 8 are disposed outside of the partitionof the tunnel 1, and housed respective in the thin-wall caps 5, 7, 9 inthe form of thin-wall casings which extend through the partition 2 andare partly exposed in the tunnel 1. Since no other components than thecarriage 3 are disposed in the tunnel 1, neither gases or fine particlesare produced in the tunnel 1, thus preventing a workpiece carried by thecarriage 3 from being contaminated. Since no gases are produced in thetunnel 1, a high degree of vacuum can be achieved in the tunnel 1.

While the O-rings are used to provide a seal between the thin-wall capsand the partition in the above embodiment, metal seals may be interposedbetween the thin-wall caps and the partition. Alternatively, thethin-wall caps may be welded to the partition to seal the vacuumcondition in the tunnel.

Inasmuch as the levitating electromagnets, the linear motors, and thedisplacement sensors are disposed outside of the tunnel, the maintenanceof the coils and the displacement sensors can be facilitated. Inaddition, the maintenance of these parts can be carried out while thevacuum condition is being kept in the tunnel.

(2nd embodiment)

A magnetic levitation conveyor apparatus according to a secondembodiment of the present invention will be described below withreference to FIGS. 4 through 6. FIG. 4 is a set of verticalcross-sectional views of tunnel structures (A), (B) of the magneticlevitation conveyor apparatus, and FIG. 5 is a plan view of the tunnelstructures. As shown in FIGS. 4(A), (B), the magnetic levitationconveyor apparatus comprises a tunnel 1 constructed of partitions with avacuum maintained therein, and a carriage 3 disposed in the tunnel 1.

In the tunnel structure (A), the partitions of the tunnel 1 include leftand right partitions 13, 14 and upper and lower partitions 15, 16. Theupper and lower partitions 15, 16 comprise respective thin plates 15a,16a in the form of stainless steel sheets (SUS304) disposed on thevacuum side for shielding the vacuum, and respective thick reinforcingplates 15b, 16b in the form of thick stainless steel sheets disposed onthe atmospheric side and rigid enough to reinforce the thin plates 15a,16a. The left and right partitions 13, 14 comprise respective thickaluminum sheets. Each of the thin plates 15a, 16a has a thickness t ofabout 1 mm.

In the tunnel structure (B), the partitions of the tunnel 1 include thinplates 13a, 14a, 15a, 16a in the form of stainless steel sheets disposedon the vacuum side and reinforcing plates 13b, 14b, 15b in the form ofrigid thick aluminum sheets disposed on the atmospheric side. The thinplates 13a, 14a, 15a, 16a are welded or brazed to each other to providea hermetic seal. The reinforcing plate 15b and the reinforcing plates13b, 14b are separate from each other, and fastened to each other by anadhesive or bolts.

In the tunnel structure (A), O-rings 11 for sealing the vacuum areinterposed between the upper and lower partitions 15, 16 and the leftand right partitions 13, 14. The upper and lower partitions 15, 16 andthe left and right partitions 13, 14 are fastened to each other by bolts10.

As shown in FIG. 6, an anchor bolt 10a is welded to the thin plate 15a,and the thin plate 15a and the reinforcing plate 15b are integrallyfastened to each other by a nut 15b threaded over the anchor bolt 10a.The thin plate 15a and the reinforcing plate 15b of the upper partition15 are integrally bonded to each other in a region other than the anchorbolt 10a. The thin plate 16a and the reinforcing plate 16b of the lowerpartition 16 are integrally bonded to each other.

Levitating electromagnets 4 for levitating and supporting the carriage 3out of contact with the partitions of the tunnel 1 are arrayed on theupper partition 15 at equal intervals in the direction in which thecarriage 3 is moved forward (see FIG. 5). The levitating electromagnets4 have magnetic poles 4a extending through the reinforcing plate 15b anddisposed adjacent to the thin plate 15a, and coils 4b disposed outsideof the reinforcing plate 15b.

Linear motors 6 composed of electromagnets for moving the carriage 3 aremounted on the lower partition 16. The linear motors 16 are arrayed atequal intervals in the direction in which the carriage 3 is movedforward. The linear motors 6 have magnetic poles 6a extending throughthe reinforcing plate 16b and disposed adjacent to the thin plate 16a,and coils 6b disposed outside of the reinforcing plate 16b. Displacementsensors 8 for detecting the vertical distance therefrom to the carriage3 are mounted on the lower partition 16.

The magnetic levitation conveyor apparatus shown in FIG. 4(A) or (B)operates as follows: The levitating electromagnets 4 are first energizedby a control circuit (not shown) to apply magnetic attractive forcesthrough the thin plate 16a to the carriage 3 with a magnetic member (notshown) disposed on an upper surface thereof for thereby levitating thecarriage 3. The distance by which the carriage 3 is lifted is detectedby the displacement sensors 8 through the thin plate 15a, and anexciting current supplied to the levitating electromagnets 4 iscontrolled depending on the output signal from the displacement sensors8. While the carriage 3 remains lifted by the levitating electromagnets4, the carriage 3 is propelled and moved by the linear motors 6 in theforward direction (the direction normal to the sheet of FIG. 1).

In this embodiment, each of at least the upper and lower partitions ofthe tunnel comprises a thin plate for shielding the vacuum and areinforcing plate which reinforces the thin plate, and the thin plateand the reinforcing plate are joined to each other by an adhesive or abolt and nut. Therefore, the partitions are highly rigid to minimize anydeformation of the tunnel. Since each of the partitions of the tunnel iscomposed of two pieces, they can be machined in a manner to match thecharacteristics of the components, can easily be machined, and can bemanufactured with a reduced cost. The number of O-rings used isminimized, and a high degree of vacuum can be achieved.

(3rd embodiment)

The structure of a conveyor passage and a carriage of a magneticlevitation conveyor apparatus according to a third embodiment of thepresent invention will be described below with reference to FIGS. 7through 16.

FIG. 7 shows the structure of a conveyor passage and a carriage. Acarriage 3 is moved in a tunnel surrounded by a partition 2 made of anonmagnetic material such as stainless steel or the like. The partition2 includes an upper partition plate 15 on which levitatingelectromagnets 4 are arrayed in two rows. Displacement sensors 8 andelectromagnets 6 of linear motors are arrayed on a lower surface of thepartition 2.

The carriage 3 has an outer shell 19 made of aluminum which serves as asecondary conductor (electrically conductive member) in a lower portionof the carriage 3 which confronts the linear motors 6. The carriage 3 isthus propelled in the direction normal to the sheet of FIG. 7.

A plate member (magnetic member) 20 made of a magnetic material ismounted on an upper surface of the outer shell 19 of the carriage 3. Asshown in FIG. 8, the magnetic member 20 has a width equal to the widthWp of the magnetic poles of the levitating electromagnets 4. Themagnetic member 20 is displaced a distance "a" in a guiding direction(the direction indicated by the arrow H in FIG. 8) toward the respectiveopposite sides of the carriage 3 (outwardly in the direction indicatedby the arrow H in FIG. 8). The distance "a" may be nil.

In FIG. 7, the displacement sensors 8 that are disposed below thecarriage 3 in confronting relation to the levitating electromagnets 4detect the vertical distance therefrom to the lower surface of thecarriage 3, and output the detected distance to a levitation controlcircuit (not shown). In response to the output signal from thedisplacement sensors 8, the levitation control circuit increases orreduces an exciting current supplied to the levitating electromagnets 4to control magnetic attractive forces acting on the plate member 20 ofmagnetic material on the upper surface of the carriage 3. Therefore, thecarriage 3 can be suspended vertically and stably levitated to a targetposition out of contact with the partition.

When the levitating electromagnets 4 are supplied with a current toapply magnetic attractive forces therefrom to the plate member 20 ofmagnetic material, since the plate member 20 of magnetic material andthe magnetic pole surfaces of the levitating electromagnets 4 arepositioned relatively to each other as described above, the plate member20 of magnetic material is subjected to forces tending to move the platemember 20 of magnetic material toward the center of the carriage 3. As aresult, the carriage 3 is passively positioned in the guiding direction(the direction H in FIG. 8).

As can be seen from FIG. 7, the outer shell 19 of the carriage 3 has acarriage opening 3-0 defined in a side wall thereof, and the partition 2has a partition opening defined in a side wall thereof. A workpiece canbe taken into and out of the carriage 3 through the carriage opening 3-0and the partition opening 2-0. The positional relation of the platemember 20 of magnetic material, the carriage 3, and the carriage opening3-0 is shown by way of example in FIG. 9.

In the embodiment shown in FIG. 7, the displacement sensors 8 are of theeddy-current type for detecting the vertical position of the lowersurface of the carriage based on an eddy current produced in the lowersurface of the carriage which is made of an aluminum plate. To preventthe partition 2 from electromagnetically affecting the displacementsensors 8, the displacement sensors 8 are encased in nonconductivesensor caps made of ceramics, for example. The carriage 3 has emergencywheels 46.

In FIG. 7, an electromagnetic brake 18 comprising an electromagnet isdisposed midway between the levitation electromagnets 4. Theelectromagnet of the electromagnetic brake 18 cooperates with a braketarget (not shown) fixed to the center of the upper surface of thecarriage 3 in defining a magnetic path for positioning the carriage 3under magnetic attractive forces.

A mount member 21 is disposed in the carriage 3 for holding asemiconductor wafer 22 or the like as a workpiece so that thesemiconductor wafer 22 will not be damaged during movement.

Although not shown, the levitating electromagnets 4 disposed on the leftand right sides of the partition 2, the linear motors 6 disposed on thelower side of the partition 2, and the displacement sensors 8 disposedon the lower side of the partition 2 in alignment with the levitatingelectromagnets 4 are arranged at equal intervals in the direction inwhich the carriage 3 is movable forward (the direction normal to thesheet of FIG. 7). The electromagnet brake 18 is disposed only in aposition where the carriage 3 is to stop. The position shown in FIG. 7is such a position where the carriage 3 is to stop, i.e., a positionwhere there is an installation for processing the wafer 22 that has beenconveyed. However, no electromagnet brake 18 is disposed in locationswhere the carriage 3 does not stop. The partition 2 is elongate in thedirection in which the carriage 3 is movable forward (the directionnormal to the sheet of FIG. 7).

In operation, while the carriage 3 is being lifted by the levitatingelectromagnets 4, the carriage 3 is propelled and move in the forwarddirection by the linear motors 6 out of contact with the partition 2. Atthe stop position, the carriage 3 is stopped by the electromagneticbrake 18, and a robot arm (not shown) or the like is used to take thewafer 22 into or out of the carriage 3 through the partition opening 2-0and the carriage opening 3-0.

As shown in FIG. 9, the plate member 20 of magnetic material in theshape of a centrally open rectangle is fixed to the upper surface of theouter shell of the carriage 3. The carriage opening 3-0 is defined ineach of the four side walls of the outer shell of the carriage 3.

The plate member 20 of magnetic material comprises, as shown in FIGS.14(A), (B), two parallel magnetic pieces 20x and two parallel magneticpieces 20y extending perpendicularly to the magnetic pieces 20x so as tocorrespond to the magnetic pole surfaces of the levitationelectromagnets arrayed in two rows.

FIG. 10 shows a branched point of the tunnel where the conveyor passageis branched orthogonally. In the branched point, the tunnel 1 isbranched along the directions M, P of movement, and two rows oflevitation electromagnets 4 are arrayed along each of main and branchedconveyor passages. Since the carriage 3 has on its upper surface theplate member 20 of magnetic material which is composed of two parallelmagnetic pieces extending in the direction in which the carriage 3conveys a workpiece and two parallel magnetic pieces extendingperpendicularly thereto, so as to correspond to the magnetic polesurfaces of the levitation electromagnets 4, it is possible for thecarriage 3 to change its directions from M to P or P to M while it isbeing levitated.

With the plate member 20 of magnetic material in the shape of acentrally open rectangle being fixed to the upper surface of thecarriage 3, as shown in FIG. 9, since the linear motors for moving thecarriage are also electromagnets for generating a moving magnetic field,if the linear motors were mounted on the center of the upper partition,then they would apply magnetic attractive forces to the plate member 20of magnetic material, which would not be preferable. The linear motorsshould preferably be positioned at the center of the carriage in view ofa space factor and stability of the thrust imposed by the linear motors.Therefore, the linear motors 6 are necessarily disposed on the centralarea of the lower partition.

The displacement sensors 8 comprise eddy-current sensors or inductivesensors, and have better sensitivity or linearity if the vertical gapbetween themselves and the target, i.e., the lower surface of thecarriage to be detected, is smaller. The carriage is required to becontrolled properly when it falls downwardly (in the direction ofgravity). Consequently, the vertical position of the carriage can becontrolled with greater accuracy by positioning the displacement sensors8 on the lower surface of the partition 2. If the displacement sensorswere mounted on the upper surface of the partition, then they would haveto be disposed between the magnetic poles of the levitationelectromagnets, and such an arrangement would require the magnetic polesto be increased in width, resulting in a larger size of the levitationelectromagnets. Therefore, the displacement sensors 8 should preferablybe disposed on the lower surface of the partition 2 in lower positionscorresponding to the levitation electromagnets. The electromagnet 18 ofthe electromagnetic brake is disposed in a remaining space, i.e., on theupper partition plate 15 of the partition 2 between the levitationelectromagnets 4. The components are thus arranged so as to provide acompact conveyor passage which is well balanced as a whole as shown inFIG. 7.

The plate member 20 of magnetic material (magnetic member) mounted onthe upper surface of the carriage will be described in detail below.FIG. 11(A) shows the positional relation between the magnetic polesurfaces 4 of the levitation electromagnets and the magnetic member 20on the upper surface of the carriage at a branched point of the conveyorpassage. The carriage to which the magnetic member 20 in the shape of acentrally open rectangle is fixed is lifted by magnetic attractiveforces produced from magnetic pole surfaces 4a, 4b of the levitationelectromagnets that are arrayed along main and branched conveyor passagealong which the carriage is movable, and is propelled by the linearmotors (not shown) to move in the tunnel while being held out of contactwith the partition. FIG. 11(A) illustrates a branched location of theconveyor passage, where the main conveyor passage in the direction M andthe branched conveyor passage in the direction P intersect with eachother. FIG. 11(C) shows in perspective the magnetic member 20 fixed tothe carriage 3. The magnetic member 20 has sides whose widths Wa, Wb aresubstantially the same as the width W of the magnetic pole of each ofthe levitation electromagnets.

FIG. 11(B) is a side elevational view of FIG. 11(A), illustrating themanner in which the carriage is lifted by the levitation electromagnets.The levitation electromagnets are arrayed on a main frame of theconveyor apparatus, and the magnetic pole surfaces 4a, 4b of thelevitation electromagnets are disposed in confronting relation to themagnetic member 20 that is fixed to the upper surface of the carriage.Each of the levitation electromagnets has a C-shaped magnetic pole. Asshown in FIG. 12(C), a closed magnetic path (magnetic flux Φ) is formedin the magnetic member 20 from the magnetic pole surfaces of theelectromagnets through the partition (not shown) and gaps. Therefore,magnetic shearing forces B are generated between the ends of themagnetic pole surfaces 4a, 4b and the ends of sides of the magneticmember 20, thus producing a so-called guiding rigidity for guiding thecarriage passively toward the magnetic center.

FIG. 12(A) is a plan view showing by way of example the positionalrelation between the magnetic member 20 fixed to the upper surface ofthe carriage and the magnetic pole surfaces 4b of the electromagnets,the view being illustrative of the magnetic pole surfaces 4b positionedat corners of the magnetic member 20 as shown hatched. FIG. 12(B) is across-sectional view taken along line A-A' of FIG. 12(A). When theelectromagnets are energized, two areas indicated at B' are located atthe magnetic poles 4b and the ends of the magnetic member 20, wheremagnetic shearing forces B are generated for guiding the carriage 3toward the magnetic center while the carriage 3 is moving in thedirection P.

The carriage to which the magnetic member 20 in the shape of a centrallyopen rectangle is fixed is moved along the main conveyor passage in thedirection M, and stopped by the non-illustrated electromagnetic brake atthe point of intersection between the main conveyor passage in thedirection M and the branched conveyor passage in the direction P. At thepoint of intersection, the magnetic pole surfaces for keeping thecarriage lifted are switched from 4a to 4b, and a propelling means suchas non-illustrated linear motors is actuated to propel the carriage inthe direction P. The carriage is now moved in the direction P along thebranched conveyor passage. While the directional change from thedirection M to the direction P has been described above, the carriagemay change its direction from P to M. Accordingly, the carriage to whichthe magnetic member in the shape of a centrally open rectangle is fixedcan change its direction easily by switching the conveyor passages towhich the electromagnets for keeping the carriage lifted belong. Aprocess of switching the electromagnets for keeping the carriage liftedwill be described in detail later on with respect to a sixth embodiment.

(4th and 5th embodiments)

FIGS. 13, 15, and 16 show magnetic levitation conveyor apparatusaccording to fourth and fifth embodiments of the present invention. FIG.13(A) shows in plan the shape of a magnetic member 20b. The magneticmember 20b which is in the shape of a centrally open rectangle compriseselements 20b1 serving as four sides and elements 20bs serving as fourcorners. These elements 20b1, 20bs are spaced by gaps "d" therebetween.Thus, the magnetic member 20b is composed of four side elements 20b1 andfour corner elements 20bs, each having ridges, with gaps "d" or groovespresent between these elements. The gaps (grooves) "d" extend in thedirection in which the carriage moves and the direction perpendicularthereto.

The four side elements 20bl have respective recesses (grooves) 24defined centrally therein which extend in the direction in which thecarriage moves and the direction perpendicular thereto. The four cornerelements 20bs also have respective recesses (grooves) 24 definedcentrally therein.

FIG. 13(B) is a sectional side elevational view showing the positionalrelation between the magnetic poles of levitation electromagnets and themagnetic member, and FIG. 13(C) is an enlarge partial view thereof.Levitation electromagnets 4a, 4b have cross-sectionally C-shapedmagnetic poles as shown each divided into magnetic pole surfaces 4b1,4b2. A magnetic flux Φ flows in a closed loop which extends from themagnetic pole 4b1 through a ridge 20b11 or 20bs1, below the groove 24,through a ridge 20b12 or 20bs2 and the magnetic pole 4b2. Each of thefour side elements and the four corner elements has a recess (groove) 24in its central region, with the gap "d" between adjacent ones of theelements. Therefore, magnetic shearing forces are produced at fourlocations indicated at D with respect to one electromagnet having across-sectionally C-shaped magnetic pole. The so-called guiding rigidityfor guiding the carriage passively to the magnetic center is greatlyincreased as compared with the first embodiment. Since the magneticmember 20b is substantially in the shape of a centrally open rectanglealso in this embodiment, the carriage can easily change its directionsat a branched point of the conveyor passage.

FIGS. 15 and 16 show modifications of the magnetic member 20. In each ofthe modifications, four corners or four sides of the magnetic membershave recesses (grooves) 24 or gaps "d" In these recesses 24 or the gaps"d", magnetic shearing forces are generated between the magnetic memberand the magnetic pole surfaces of cross-sectionally C-shaped magneticpoles of levitation electromagnets, thus increasing so-called guidingrigidity for guiding the carriage passively to the magnetic center undermagnetic centripetal forces. Since the magnetic member is substantiallyin the shape of a centrally open rectangle also in these modifications,the carriage can easily change its directions at a branched point of theconveyor passage.

(6th embodiment)

Changing the directions of a carriage of a magnetic levitation conveyorapparatus according to a sixth embodiment of the present invention, at abranched point having substantially orthogonal branched passages will bedescribed below with reference to FIGS. 17 through 24.

As shown in FIGS. 17 and 18, the magnetic levitation conveyor apparatushas a number of arrayed levitation electromagnets 4, a conveyor passage23 including a main conveyor passage 23a and branched conveyor passages23b, 23c branched from the main conveyor passage 23a at a branched point26, a carriage 3 levitated under magnetic forces from the levitationelectromagnets 4 and movable by propelling forces generated by linearmotors (not shown) along the conveyor passage 23 in a tunnel (not shown)defined by a partition, and a switching means 25 for changing thedirections of movement of the carriage 3 at the branched point 26. Theswitching means 25 includes a plurality of (four in FIGS. 7 and 8)levitation electromagnets 4 arrayed in the direction of the mainconveyor passage 23a and a plurality of as many levitationelectromagnets 4 arrayed in another direction and disposed adjacentrespectively to the above levitation electromagnets 4. When the carriage3 reaches the branched point 26 from one of the conveyor passages (e.g.,the main conveyor passage 23a), the switching means 25 switchessuccessively from one set of levitation electromagnets (e.g.,electromagnets 4x) in an operative condition to the other set oflevitation electromagnets (e.g., electromagnets 4y) in an inoperativecondition.

The main conveyor passage 23a is oriented in a main conveying directionC, and the branched conveyor passages 23b, 23c are oriented inrespective directions D, E perpendicular to the main conveying directionC in a T-shaped or cross-shaped pattern. Only one of the branchedconveyor passages 23b, 23c may be employed, and the branched conveyorpassages 23b, 23c may be oriented not perpendicularly to the mainconveying direction C. If the branched conveyor passages 23b, 23c wereoriented not perpendicularly to the main conveying direction C, then thelevitation electromagnets would be arrayed out of alignment with theperpendicular directions. Therefore, the branched conveyor passages 23b,23c should be oriented at about 90° with respect to the main conveyingdirection C.

As shown in FIGS. 17 through 19, a pair of left and right rows oflevitation electromagnets 4, which serve as magnetic bearings and arealso called levitation magnetic poles, are arrayed on a lower surface ofa main frame 27 of the conveyor passage 23 at a predetermined pitch inthe conveying direction C, D, or E. Each of the electromagnets 4, as aprimary side, comprises a coil and a magnetic yoke, whereas the magneticmember 20, as a secondary side, described in detail in the previousembodiment, is mounted on the peripheral edge of an upper surface of thecarriage 3, the magnetic member 20 being composed of a yoke which servesas a target to be levitated. The magnetic member 20 is positioned belowthe electromagnets 4 with a non-illustrated tunnel partition interposedtherebetween so that the carriage 3 can be lifted out of contact withthe tunnel under magnetic attractive forces produced by theelectromagnets 4. The electromagnets 4 as the primary side and themagnetic member 20 as the secondary side jointly constitute an array ofmagnetic levitation devices extending in the conveying directions C, D,E.

The carriage 3 is moved when propelled out of contact with the partitionby non-illustrated linear motors. The linear motors include respectivestators (electromagnets) arrayed on a lower surface of a tunnelpartition. An electrically conductive member such as an aluminum plateis mounted on a lower surface of the carriage 3. A spatial movingmagnetic field generated by the stators of the linear motors causes aneddy current to be produced in the electrically conductive membermounted on the lower surface of the carriage 3, which is then subjectedto propelling forces to move the carriage 3 out of contact with thetunnel partition.

Only those of the levitation electromagnets 4 which are required to liftthe carriage 3 are energized. Specifically, the arrayed electromagnets 4are switched successively into and out of an operative condition alongthe direction in which the carriage 3 is to move, according to adetected signal indicative of the position of the carriage, therebyswitching the magnetic poles on and off to successively generatemagnetic attractive forces applied to the magnetic member 20 on thecarriage 3. The carriage 3 now moves in the conveying direction C, D, orE while keeping a predetermined gap below the lower surface of thepartition of the conveyor passage. Switching of the levitationelectromagnets as the carriage moves will be described in detail lateron with respect to an eighth embodiment of the present invention.

A mechanical arrangement of the switching means 25 which is operated atthe branched point 26 will be described below with reference to FIG. 20.At the branched point 26, electromagnets 4x arrayed in the direction ofthe main conveying passage 23a at regular intervals in the sameorientation as the levitation electromagnets 4 in the main conveyorpassage 23a, and electromagnets 4y arrayed in the directions of thebranched conveying passages 23b, 23c at regular intervals in the sameorientations as the levitation electromagnets 4 in branched conveyingpassages 23b, 23c are mounted on an upper partition surface of thetunnel with the magnetic pole surfaces facing downwardly. Theelectromagnets 4x, 4y are positioned perpendicularly to each other anddisposed adjacent to each other to prevent the carriage from vibratingwhen the levitation electromagnets are switched to change the conveyingdirections. Displacement sensors 8 for detecting the levitated positionof the carriage 3 are mounted on a tunnel partition (not shown) directlybelow the respective levitation electromagnets 4x, 4y.

FIG. 21 shows in block form a control system for the levitationelectromagnets of the magnetic levitation conveyor apparatus. A processfor controlling the switching on and off of the magnetic poles to liftthe carriage and the levitated position of the carriage will bedescribed below with reference to FIG. 21.

A control circuit 28 is a closed-loop control circuit for controlling anexciting current to be supplied to the levitation electromagnets 4xbased on an output signal from the displacement sensors 8. The signalfrom the displacement sensors 8 which is indicative of the detectedlevitated position (displacement) of the carriage 3 is amplified by asensor amplifier 31. The gain of the control circuit 28 which is presetby a control unit 29 is adjusted by a gain controller 32. The detectedlevitated position is compared with a target levitation value which ispreset by the control unit 29 by a target levitation value controller33. A compensating circuit 34 adjusts the phase of the closed-loopcontrol circuit. An output signal from the compensating circuit 34 isamplified by a power amplifier 35, and the amplified signal is suppliedas an exciting current to the levitation electromagnets 4x. Thelevitation electromagnets 4x then generate magnetic attractive forcescorresponding to the supplied exciting current, for thereby attractingthe magnetic member target on the carriage 3 to control the levitatedposition of the carriage 3.

The control unit 29 comprises an A/D converter 37, a D/A converter 39, acontrol signal generator 40 for generating a gain signal and a targetlevitation value signal, and a CPU 38. The control unit 29 serves tocontrol the switching on and off of the magnetic poles to lift thecarriage 3. After the output signal from the displacement sensors 8 isamplified by the sensor amplifier 31, it is converted by the A/Dconverter 37 into a digital signal which is supplied to the CPU 38 fordetecting the position of the carriage 3 with respect to the magneticpoles to lift the carriage 3. For example, the control unit 29 canproduce a signal indicative of a detected carriage position forswitching a certain levitation electromagnet from an inoperativecondition into an operative condition to lift the carriage as it moves.The control signal generator 40 supplies the gain controller 32 and thetarget levitation value controller 33 respectively with a signalindicative of a loop gain of the control circuit 28 and a signalindicative of a target levitation value of the carriage 3. Therefore,when the gain is varied from 0 to a certain preset value (or when thetarget levitation value is varied from a certain preset valuecorresponding to an inoperative condition to a certain preset valuecorresponding to an operative condition) by the control signal generator40, a levitation electromagnet can be switched from an inoperativecondition into an operative condition with the given gain and targetlevitation value.

As shown in FIG. 26, the levitation electromagnets and the displacementsensors arrayed in the direction in which the carriage moves aresuccessively switched on and off in that direction as the carriagemoves, for thereby keeping the carriage lifted. The magnetic levitationconveyor apparatus has eight control circuits for detecting thelevitated position with sensor amplifiers 8 and lifting the carriage toa target position with the energization of power amplifiers 35 tocontrol adjacent four pairs of electromagnets of the two rows ofelectromagnets. The pairs of electromagnets to be controlled areselected when switches 42 are closed according to a signal from aselective signal generator 41.

When the levitation electromagnets 4 in the main conveyor passage 23aare controlled by a control signal from the control unit 29 and thecontrol circuit 28, the magnetic member 20 is attracted by magneticattractive forces produced by the energization of the levitationelectromagnets 4, lifting the carriage 3, and the carriage 3 ispropelled by the linear motors to move in the direction C in the mainconveyor passage 23a until it arrives at the branched point 26. If thecarriage 3 is to move straight in the main conveyor passage 23a, thenthe electromagnets 4x of the switching means 25 at the branched point26, which are arrayed in the direction of the main conveyor passage, arecontrolled in the same manner as the levitation electromagnets 4. Thecarriage 3 as it remains lifted passes through the branched point 26,and is transferred to and lifted by the levitation electromagnets 4 in aforward section of the main conveyor passage 23a. The carriage 3 iscontinuously moved by switching these levitation electromagnetsaccording to a signal representative of a detected carriage position.If, however, the direction of the carriage 3 is to change from thedirection C of the main conveyor passage 23a to the direction D or E ofthe branched conveyor passage 23b or 23c at the branched point 26, thenthe switching means 25 is controlled by the control unit 29 and thecontrol circuit 28 as follows:

A switching sequence will be described below with reference to FIGS. 22and 23. Reference characters I, III, 1, 3 in FIGS. 22(A) through (D)represent positions of electromagnets 4x arrayed in the direction of themain conveyor passage, and reference characters I', III' 1', 3'represent positions of electromagnets 4y arrayed in the direction of thebranched conveyor passage.

As shown in FIG. 22, when the carriage 3 arrives at the branched point26, the carriage 3 is supported out of contact with the tunnel partitionwhile remaining levitated by magnetic attractive forces and guidingrigidity produced by the electromagnets 4x that are controlled to liftthe carriage 3 in the main conveying direction and located at thepositions indicated by I, III, 1, 3 (the condition shown in FIG. 22(A)).

The control signal generators 40 of levitation control systems (loops)associated with the electromagnets 4y located at the positions indicatedby III', 1' output a target levitation voltage, the gain of thelevitation control systems are set to 0, and switches 42 which have beenopen are closed.

The gain is progressively increased from 0 to a preset value for anoperative condition over a preset period of time by the control signalgenerators 40 of the levitation control systems (loops) associated withthe electromagnets 4y located at the positions indicated by III', 1',thereby gradually flowing a current to the electromagnets 4y to put theelectromagnets 4y into an operative condition. At the same time, thegain is progressively decreased from a preset value for an operativecondition to 0 over a preset period of time by the control signalgenerators 40 of levitation control systems (loops) associated with theelectromagnets 4x located at the positions indicated by III, 1, afterwhich the switches 42 which have been closed are opened (see FIG. 22(B),FIG. 23).

After elapse of a preset waiting time, the control signal generators 40of levitation control systems (loops) associated with the electromagnets4y located at the positions indicated by I', 3' output a targetlevitation voltage, the gain of the levitation control systems are setto 0, and switches 42 which have been open are closed.

The gain is progressively increased from 0 to a preset value for anoperative condition over a preset period of time by the control signalgenerators 40 of the levitation control systems (loops) associated withthe electromagnets 4y located at the positions indicated by I', 3',thereby gradually flowing a current to the electromagnets 4y to put theelectromagnets 4y into an operative condition. At the same time, thegain is progressively decreased from a preset value for an operativecondition to 0 over a preset period of time by the control signalgenerators 40 of levitation control systems (loops) associated with theelectromagnets 4x located at the positions indicated by I, 3, afterwhich the switches 42 which have been closed are opened (see FIG. 22(C),FIG. 23).

Through the above sequence, the carriage 3 is now suspended by magneticattractive forces generated by the four electromagnets 4y that are newlycontrolled to lift the carriage 3 and located at the positions indicatedby I', III', 1', 3' (see FIG. 22(D)). The magnetic poles to lift thecarriage 3 are now switched from the electromagnets 4x arrayed in themain conveying direction, which have initially been magnetic poles tolift the carriage 3, to the electromagnets 4y arrayed in the directionof the branched conveyor passage which is angularly spaced about 90°from the main conveying direction. The carriage 3 moves in the directionD or E of the branched conveyor passage 23b or 23c In this embodiment,when the gains of the electromagnets 4x, 4y at the branched point 26 arecontrolled, diagonally opposite electromagnets are handled as sets, andthey are switched from III to III' and from 1 to 1' at the same time,and then switched from I to 3' and from 3 to I' at the same time. Sincethe gains are gradually changed in a crossover relation to each other,any vibration which the carriage 3 tends to suffer upon switching cangreatly be reduced.

In the above embodiment, the control means has been described whichcauses the control unit 29 to gradually change the gains of the controlcircuits over the preset periods of time when the levitationelectromagnets in an operative condition are brought into an inoperativecondition and the levitation electromagnets in an inoperative conditionare brought into an operative condition. The same result can be achievedby causing the control unit 29 to gradually vary the target levitationvoltage representative of a target levitation value for the carriage, orby gradually varying the gains of the control circuits andsimultaneously gradually varying an offset voltage representative of atarget levitation value for the carriage. In FIG. 23, the voltageindicative of the gain or the target levitation value is linearly variedin a time t₀. However, the voltage may be varied along a curve, as shownin FIG. 24(A) or 24(B).

When the levitation electromagnets in an operative condition are broughtinto an inoperative condition and the levitation electromagnets in aninoperative condition which are arranged in a different conveyingdirection are brought into an operative condition, closestelectromagnets in operative and inoperative conditions, respectively,are handled as a set and switched from one to the other. In the abovesequence, the two sets of electromagnets are switched from III to III'and from 1 to 1' at the same time, and then from I to 3' and from 3 toI' at the same time.

However, the electromagnets may be switched in various combinations ofsets. For example, sets of electromagnets may be switched from III toIII', then from 1 to 1', then from I to 3', and finally from 3 to I'. Byprogramming the control unit 29 to select a suitable sequence forswitching sets of electromagnets, it is possible to select an optimumcombination of sets of electromagnets while observing how the carriagevibrates upon switching.

Since the electromagnets are switched from magnetic poles which arecontrolled to lift the carriage to those magnetic poles which areangularly spaced about 90° from the magnetic poles, the carriage canmove in a T-shaped or cross-shaped pattern. Inasmuch as the gains of themagnetic poles are controlled in a crossover relation to each other, anyvibration which the carriage tends to suffer upon switching caneffectively be reduced.

The carriage 3 can also be easily controlled to move from the branchedconveyor passage 23b or 23c to the main conveyor passage 23a.

According to this embodiment, the direction of the carriage 3 can beswitched to a desired one of the branched conveyor passages 23b, 23cother than the main conveyor passage 23a, and hence the carriage 3 canbe moved with 2 degrees of orthogonal freedom while being lifted in ahorizontal plane.

(7th embodiment)

Switching levitation electromagnets for suspending a carriage as itmoves according to a seventh embodiment of the present invention will bedescribed below with reference to FIGS. 25 through 30.

FIG. 25 is a cross-sectional view along a conveyor passage of the abovemagnetic levitation conveyor apparatus. The carriage 3 is propelled bythe linear motors 6 to move in the direction indicated by the arrow in atunnel defined by a partition while it remains lifted by levitationelectromagnets 4₁, 4₂, . . . At this time, the levitation electromagnets4₃, 4₅ are in an operative condition, and the levitation electromagnets4₁, 4₂, 4₄, 4₆, 4₇, 4₈, 4₉ are in an inoperative condition. As thecarriage 3 moves, an exciting current is supplied to these levitationelectromagnets to switch their magnetic poles from an inoperativecondition to an operative condition, and cut off to switch theirmagnetic poles from an operative condition to an inoperative condition,for keeping the carriage lifted while the carriage is moving. Forexample, when the carriage 3 is moved to the left from the illustratedposition, the magnetic poles 4₂, 4₄ are switched from an inoperativecondition to an operative condition, and the magnetic poles 4₃, 4₅ areswitched from an operative condition to an inoperative condition.

FIG. 26 show in block form a control system of the magnetic levitationconveyor apparatus. The levitated position of the carriage and theswitching of the magnetic poles between operative and inoperativeconditions are controlled by the block diagram of FIG. 26. A signal fromdisplacement sensors 8₁, 8₅, . . . is amplified by a sensor amplifier31, and the gain of a control circuit loop is adjusted by a gain settingunit 32. The gain is compared with a preset voltage by a targetlevitation voltage setting unit 33 to achieve a given target levitationvalue. The phase is adjusted by a compensating circuit 34, and an outputsignal from the compensating circuit 34 is amplified by a poweramplifier 35, which supplies an exciting current to the magnetic poles4₁, 4₅, . . . of the levitation electromagnets. The magnetic levitationconveyor apparatus has eight control circuits (for four pairs of rows ofelectromagnets as the electromagnets are arrayed in two rows in eachconveyor passage) each including the components ranging from the sensoramplifier 31 to the power amplifier 35. Only a control circuit for apair of rows of levitation electromagnets 4₁, 4₅, . . . is illustrated.The levitation electromagnets 4₂, 4₃, 4₄, 4₆, 4₇, . . . are controlledby non-illustrated control circuits. In the closed-loop control circuit,the target levitated position for the carriage and the gain of thecontrol loop are given by a signal from a gain/target levitation voltagesignal generator 40. The magnetic poles are switched from an operativecondition to an inoperative condition or from an inoperative conditionto an operative condition by amplifying a signal from the displacementsensors 8₁, 8₂, . . . with the sensor amplifier 31, converting theamplified signal into a digital signal with an A/D converter, andapplying the digital signal to a control unit. Specifically, movement ofthe carriage 3 is detected by a signal from the displacement sensors 8₁,8₂, . . . , and a position selection signal is generated for switchingthe magnetic poles from an inoperative condition to an operativecondition or from an operative condition to an inoperative condition. Asignal indicative of the gain of the control circuit or a targetlevitation voltage is applied from the gain/target levitation voltagesignal generator 40 to the gain setting unit 32 and the targetlevitation value controller 33 for thereby controlling each of themagnetic poles to switch between operative and inoperative conditions.

FIG. 27 is a diagram showing a sequence of switching conventionallevitation magnetic poles. Levitation magnetic poles arranged in thedirection of movement of the carriage are successively switched from anoperative condition to an inoperative condition in that directionthrough the selective signal generator 41 and the switch group 42 as thecarriage moves. When the levitation magnetic poles are thus switched, acontrol time in which the gain varies from a preset value to 0 or from 0to a preset value with respect to each individual magnetic pole is setdepending on the speed at which the carriage moves, and the controltimes are individually varied gradually to bring the magnetic poles froman operative condition to an inoperative condition or from aninoperative condition to an operative condition for thereby successivelyswitching the levitation magnetic poles.

FIG. 28(A) is a diagram illustrative of switching of the conventionalmagnetic poles from an inoperative condition to an operative condition.In this example, when switches of the switch group 42 are closed, andthe gain varies from 0 to a preset value V₁ (from a target levitationvalue V_(s1) to a target levitation value V_(s2)) in a control time t₁,the magnetic poles are switched from an inoperative condition to anoperative condition. FIG. 28(B) is a diagram illustrative of switchingof the conventional magnetic poles from an operative condition to aninoperative condition. In this example, when switches of the switchgroup 42 are opened, and the gain varies from a preset value V₂ to 0(from the target levitation value V_(s2) to the target levitation valueV_(s1)) in a control time t₂, the magnetic poles are switched from anoperative condition to an inoperative condition. Heretofore, asdescribed above, the magnetic poles arranged in the conveying directionare individually switched from an inoperative condition to an operativecondition or from an operative condition to an inoperative condition asthe carriage moves.

The magnetic levitation conveyor apparatus requires that the carriagemove smoothly in the conveyor passage and be started and stopped assmoothly as possible. One problem which is imposed more severely at thistime is that the carriage itself tends to vibrate upon switching of thelevitation magnetic poles. According to the present invention, there isdisclosed a process of switching levitation electromagnets for movingthe carriage smoothly while solving the problem of vibration of thecarriage in switching the levitation electromagnets from an operativecondition to an inoperative condition or from an inoperative conditionto an operative condition.

In this embodiment, when levitating electromagnets arrayed in thedirection in which the carriage moves are successively switched from anoperative condition to an inoperative condition or from an inoperativecondition to an operative condition as the carriage moves, switching ofat least one set of magnetic poles arranged in that direction isgradually carried out simultaneously from an operative condition to aninoperative condition and from an inoperative condition to an operativecondition.

FIG. 29 shows the manner in which switching of one set of adjacentmagnetic poles arranged in the direction in which the carriage moves isgradually carried out simultaneously from an operative condition to aninoperative condition and from an inoperative condition to an operativecondition at the time the levitation electromagnets are successivelyswitched from an operative condition to an inoperative condition or froman inoperative condition to an operative condition. In FIG. 26, when thecarriage 3 moves to the left, the displacement sensor 8₂ associated withthe magnetic pole 4₂ detects arrival of the carriage 3. As shown in FIG.29, the magnetic pole 4₃ and the magnetic pole 4₂ which is positionedadjacent thereto in the conveying direction are gradually switchedsimultaneously from an operative condition to an inoperative conditionand from an inoperative condition to an operative condition,respectively. The switching operation gradually progresses in thecontrol time t₀. While the switching operation shown in FIG. 29 islinear, it may be effected along curves as shown in FIG. 30(A) or 30(B).

The process of controlling the switching of the levitationelectromagnets is carried out in the control system shown in FIG. 26 bygradually increasing the total gain of the control circuit from 0 to apreset value V₂ for the magnetic pole 4₂ and gradually reducing thetotal gain from a present value V₁ to 0 for the magnetic pole 4₃ withthe gain setting unit 32. The target levitation value controller 33 mayincrease an offset voltage, which is a parameter of a target levitationvoltage, from a value V_(s1) to a preset value V_(s2) for the magneticpole 4₂, and reduce the offset voltage from a present value V_(s3) to avalue V_(s4) for the magnetic pole 4₃ simultaneously gradually in thecontrol time t_(o), Alternatively, the gain of the control circuit maybe varied by the gain setting unit 32, and then the offset voltage whichis a target levitation value of the target levitation value controller33 may be varied.

In the above description, one set of magnetic poles arranged in theconveying direction, i.e., the magnetic poles 4₂, 4₃ are simultaneouslyswitched from an inoperative condition to an operative condition andfrom an operative condition to an inoperative condition, respectively.Such simultaneous magnetic pole switching operation can be carried outwith respect to a plurality of sets of magnetic poles for improvedstability of movement of the carriage.

For example, it is possible to simultaneously switching the set ofmagnetic poles 4₄, 4₅ other than the set of magnetic poles 4₂, 4₃.Specifically, the displacement sensor 8₂ detects arrival of the carriage3 as it moves thereto, and opens and closes switches through theselective signal generator 41 and the switch group 42 to switch themagnetic poles 4₂, 4₄ from an inoperative condition to an operativecondition and the magnetic poles 4₃, 4₅ from an operative condition toan inoperative condition simultaneously gradually in the control timet₀. The stability of movement of the carriage can be increased by thussimultaneously gradually switching the two sets of magnetic poles 4₂,4₃, 4₄, 4₅ which are arranged in the conveying direction.

In FIG. 25, the carriage 3 is lifted by three magnetic poles arranged inthe conveying direction. If the carriage 3 is lifted by more magneticpoles, e.g., four or five magnetic poles, then three sets of magneticpoles can be switched simultaneously. Therefore, magnetic poles cansimultaneously be switched from an operative condition to an inoperativecondition and from an inoperative condition to an operative condition invarious combinations. It is possible in such a case to select a suitablecombination of magnetic poles for simultaneous switching, and to reduce,with a selected combination, more effectively any vibration of thecarriage which is produced upon switching of levitation magnetic polesas the carriage moves.

In this embodiment, as described above, the levitation magnetic polesfor lifting and moving the carriage of the magnetic levitation conveyorapparatus are simultaneously switched gradually between operative andinoperative conditions. Consequently, the carriage is prevented fromvibrating upon switching of levitation magnetic poles as the carriagemoves, and the levitation magnetic poles can smoothly be switched at thetime the carriage is moved, stopped, or started, for thereby moving thecarriage smoothly.

(8th embodiment)

Control of the lifting/landing of a carriage according to an eighthembodiment of the present invention will be described below withreference to FIGS. 31 through 33.

In the above magnetic levitation conveyor apparatus, only the powersupply of a control device is turned on and off to lift the carriage offand land the carriage on a lower partition surface of the tunnel.Therefore, the carriage tends to be lifted or landed abruptly. Statedotherwise, when the carriage is lifted or landed, a workpiece carried bythe carriage is subjected to a shock, and liable to suffer damage.Inasmuch as the magnetic levitation conveyor apparatus is designed foruse in conveying various a workpiece such as a wafer, which is highlysusceptible to cracks, in semiconductor fabrication factories, anydamage to the workpiece poses a very serious problem. Abrupt lifting orlanding is also responsible for producing dirt and dust particles, whichare apt to lower the yield of semiconductors. When a workpiece such as awafer is conveyed, it is preferable for the vertical height of theworkpiece to be variable so that the workpiece can be received andtransferred easily. In the magnetic levitation conveyor apparatus, it isdesirable for the carriage to be lifted a distance that can freely beadjusted. If any workpiece is placed on the carriage, the carriageshould preferably be lifted from a landed condition within a shortperiod of time, so that the time required to convey a workpiece can beshortened.

The present embodiment is designed to solve the above problems, anddiscloses a magnetic levitation conveyor apparatus which can lessenshocks produced when a carriage is lifted and landed, and can freelyadjust the distance that the carriage can be lifted and the timerequired to lift and land the carriage.

FIG. 31 shows a basic arrangement of a control system. Basic operationof the control system for controlling magnetic attractive forcesproduced by levitation electromagnets 4 to lift a carriage 3 up to atarget position is the same as with the sixth and seventh embodimentsdescribed above, and will not be described below.

An output signal V_(s) from displacement sensors 8 is compared with anoffset voltage V_(f) which is a target levitation value by an adder 43,and the difference is applied to a gain setting unit 32 for determiningan amplification factor K_(p) of a control system of a control circuitcomposed of components ranging from the displacement sensors 8 to apower amplifier 35. Specifically, an output signal from the gain settingunit 32 is led to a phase compensator 34 and then to the power amplifier35 for increasing or reducing an exciting current to be supplied tocoils wound around levitation electromagnets 4. The electromagnets 4apply magnetic attractive forces generated by the exciting currentflowing through the coils to the carriage 3, which is then lifted underthe magnetic attractive forces. The carriage can be supported withgreater magnetic bearing rigidity by setting a high amplification factorin a stable range with the gain setting unit 32.

In an offset voltage supply means 33, a command is given from a program40 to a digital processing means (CPU) 38 to generate an offset voltageV_(of). The digital processing means 38 has a function as a generatingmechanism for determining an offset voltage.

Any of various programs indicated at 40 can freely be incorporated inthe digital processing means 38, and the program 40 can freely bechanged. The program 40 is generated such that the offset voltageapplied from the offset voltage supply means to the adder 43 will havedesired various characteristics (e.g., time characteristics). Since aprocess of generating such a program is a known software generationprocess, it will not be described below.

When the carriage is to be lifted, the offset voltage V_(of) and time"t" should preferably be related to each other (time characteristics) asshown in FIG. 33. Upon elapse of a time t₀ in FIG. 33, the offsetvoltage V_(of) becomes 0 V, and the carriage 3 is stably lifted in areference levitated position which is fixed by the control circuit(compensating circuit) 28.

By generating a program which achieves such time characteristics of theoffset voltage V_(of) and incorporating the program in the digitalprocessing means 38, the non-illustrated offset voltage generatingmechanism is operated to apply the offset voltage V_(of) of timecharacteristics shown in FIG. 33 to the adder 43.

When the carriage is to be landed, the offset voltage V_(of) shouldpreferably have time characteristics as shown in FIG. 32. By carryingout the same processing as described above, the offset voltage V_(of) oftime characteristics shown in FIG. 32 is applied to the adder 43.

It is also possible to have the horizontal axis (time base) of FIGS. 32and 33 represent the entire time required to fabricate a semiconductor,vary the offset voltage V_(of) in a manner to correspond to a desiredchange in the lifted distance at the time the carriage arrives at eachprocessing station, generate time characteristics over the overallfabrication process, and program such time characteristics. With such anarrangement, no shocks are produced when the carriage is lifted andlanded, and a workpiece can smoothly be received and transferred at eachprocessing station.

The levitated position of the carriage 3 is controlled such thatvertical magnetic attractive forces applied to the carriage 3 by theelectromagnets 4 and the gravity on the carriage 3 are equalized to eachother. Specifically, since an input signal supplied to the phasecompensator 34 determines an exciting current to be supplied to theelectromagnets 4, if the ratio of a change in the levitated position ofthe carriage 3 to the distance between the carriage 3 and the magneticpole surfaces of the electromagnets 4 is relatively small, then a changein leakage fluxes of a magnetic circuit composed of the electromagnets 4and the carriage 3 is small, and if the weight of the carriage 3 remainsunchanged, the input signal supplied to the phase compensator 34 as aresult of the controlling operation remains generally unchanged.

The input signal (represented by V_(p)) supplied to the phasecompensator 34 is determined by an output signal (represented by V_(s))from the displacement sensors 8, an output signal 1 (offset voltagerepresented by V_(f)) supplied to the adder 43 from a digital-to-analogconverter 44 of the control unit 29, which is an offset voltage/gainsetting output supply means, and an amplification factor (represented byK_(p)) set by the gain setting unit 32 from an output signal 2 from adigital signal output means 45 of the control unit 29. The input signalV_(p) is expressed according to the following equation:

    V.sub.p =K.sub.p ×(V.sub.s -V.sub.f)                 (1).

The D/A converter 44 and the digital signal output means 45 performtheir functions in response to a command from the digital processingmeans (CPU) 38. The processing sequence carried out by the digitalprocessing means 38 can freely be set up and modified according to theprogram 40. Consequently, the input voltage V_(p) applied to the phasecompensator 34 can freely be set according to the program 40.

As described above, when the ratio of a change in the levitated positionof the carriage 3 to the distance between the carriage 3 and themagnetic pole surfaces of the electromagnets 4 is relatively small, theinput voltage V_(p) applied to the phase compensator 34 is maintained ata constant level. Therefore, in order to vary the levitated position ofthe carriage 3 (vary the sensor output voltage V_(s)) at the time theamplification factor K_(p) is constant, the offset voltage V_(f) may bevaried under the condition defined by the equation (1). When the offsetvoltage V_(f) is constant, the amplification factor K_(p) of the gainsetting unit 32 may be varied in the same fashion.

If the levitated position of the carriage 3 undergoes a large change,then leakage fluxes from the magnetic circuit composed of theelectromagnets 4 and the carriage 3 varies greatly, and the number ofeffective magnetic fluxes for applying magnetic attractive forces to thecarriage 3 is increased or reduced to a large extent. Therefore, theratio between the exciting current supplied to the electromagnets 4 andthe magnetic attractive forces acting on the carriage 3 varies largely.

If the distance between the carriage 3 and the magnetic pole surfaces ofthe electromagnets 4 increases greatly, then since more leakage fluxesare produced, it is necessary to increase the exciting current suppliedto the electromagnets 4 for bearing the carriage 3. This results in alarge reduction in the loop gain of the magnetic levitation controlsystem which is composed of the electromagnets 4, the carriage 3, thedisplacement sensors 8, and the control circuit 28, thereby impairingstable levitation of the carriage 3.

When this happens, the carriage 3 cannot remain stably lifted only byadjusting the offset voltage V_(f). However, when the amplificationfactor K_(p) of the gain setting unit 32 is increased, the reduction inthe loop gain of the magnetic levitation control system can becompensated for, thereby keeping stable levitation of the carriage 3. Ifthe distance between the carriage 3 and the electromagnets 4 is reduced,then it can be compensated for by carrying out the above processinversely.

With the above arrangement of this embodiment, the levitated position ofthe carriage 3 can be set to any desired position by varying theamplification factor K_(p) of the gain setting unit 32 and the offsetvoltage V_(f).

Accordingly, in addition to the fact that shocks produced when thecarriage is lifted and landed can be lessened, the distance that thecarriage is lifted and the time required for the carriage to be liftedand landed can be adjusted. In the case where the magnetic levitationconveyor apparatus is incorporated in a semiconductor fabrication line,a workpiece such as a wafer are prevented from being damaged, and dirtand dust particles are prevented from being produced, resulting in anincreased yield of semiconductors. At the same time, a workpiece cansmoothly be received and transferred between lower stations and thecarriage for increased conveying efficiency.

(9th embodiment)

A passive damper disposed in a conveyor passage according to a ninthembodiment will be described below with reference to FIG. 34. Thepassive damper according to this embodiment serves to absorb and dampenvibrations of a carriage when the carriage vibrates in a directionperpendicular to a conveyor passage when the carriage is moving in atunnel while magnetically levitated.

The carriage suspended by levitation electromagnets is supported in aguiding direction by so-called guiding rigidity which is provided byspring forces produced by the electromagnets as described in detail withrespect to the third embodiment. Therefore, if some external forces areapplied to the carriage and the carriage is vibrated in a Y direction,then the vibrations of the carriage are not stopped as no dampeningforces are imposed. Particularly when the moving carriage is to bestopped by an electromagnetic brake in the vicinity of a point where thecarriage is to be stopped, the carriage suffers large vibrations andimpinges upon a partition, producing metallic powder, or a waiting timehas to be consumed before a workpiece is loaded into the carriagebecause a long period of time is needed to stop the vibrations of thecarriage. The passive damper according to this embodiment is capable ofquickly absorbing vibrations in a direction (guiding direction)perpendicular to the direction in which the magnetically levitatedcarriage is conveyed.

In a conveyor apparatus shown in FIG. 34, a carriage 3 disposed in atunnel (not shown) defined by a partition is suspended by magneticattractive forces generated by electromagnets 4 disposed in a conveyorpassage 23, and moved in a conveying direction along the conveyorpassage. In FIG. 34, X-, Y-, and Z-axes represent three-dimensionalcoordinate axes extending perpendicularly to each other. An X directionindicates the conveying direction, a Y direction indicates lateraldirections perpendicular to the X direction, and a Z direction indicatesthe direction of magnetic attractive forces perpendicular to the X and Ydirections, i.e., the direction normal to magnetic pole surfaces 4n ofthe electromagnets 4.

The conveyor apparatus has a passive damper comprising a support device51 which supports the electromagnets 4 while holding them in a certainposition with respect to the direction Z of attractive forces and theconveying direction X, and supports the electromagnets 4 movably withrespect to the lateral directions Y perpendicular to the conveyingdirection X. The electromagnets 4, as a primary side, are arrayed atgiven intervals in the conveying direction X, and serve as magneticbearings and are also called levitation magnetic poles. A magneticmember target (magnetic member) 20, as a secondary side, is mounted onthe peripheral edge of an upper surface of the carriage 3, the magneticmember 20 being composed of a yoke which serves as a target to belevitated. The magnetic member 20 is positioned below the electromagnets4 with a non-illustrated tunnel partition interposed therebetween sothat the carriage 3 can be lifted out of contact with the tunnel undermagnetic attractive forces produced by the electromagnets 4 which areenergized. The electromagnets 4 as the primary side and the magneticmember 20 as the secondary side jointly constitute a magnetic bearingdevice composed of an array of magnetic bearings extending in theconveying direction X.

The support device 50 of the passive damper will be described below. Alinear rail 52 extending in the lateral directions (Y direction) isdisposed on a fixed wall 27 of a main frame at a stop position or thelike in the conveyor passage. A linear bearing 53 is mounted on theupper end of each of the levitation electromagnets 4 for slidingmovement to any desired position only in the Y direction along thelinear rail 52. The linear rail 52 and the linear bearing 53 jointlyserve as a linear guide support device 51 having a degree of freedom inthe Y direction. Each of the levitation electromagnets 4 is movable withthe linear bearing 53 only in the Y direction, and has no play and isnot movable about the X and Z directions and not rotatable around theX-, Y-, and Z-axes. Therefore, each levitation electromagnet 4 has nodegree of motion freedom about the X and Z directions and around the X-,Y-, and Z-axes, and has a degree of translation freedom that can be setas desired in the Y direction.

The support device 51 holds the levitation electromagnet 4 in a certainposition in the Y direction with fixed walls 27a of the main frame thatare disposed in confronting relation to the conveyor passage, and a pairof springs 54 and a pair of dashpots 55, as a dampening force applyingmeans, which are disposed between the fixed walls 27a and theelectromagnet 4 that is positioned between the fixed walls 27a. Alubricant applied between the linear rail 52 and the linear bearing 53also serves as the dampening force applying means because the viscosityof the lubricant and the frictional resistance of sliding portions ofthe linear rail 52 and the linear bearing 53 produce dampening forces.When the electromagnet 4 vibrates in the Y direction through the linearguide unit, the lubricant can dampen vibrations of the electromagnet 4in the Y direction. However, the lubricant alone is not effective enoughto produce sufficient dampening forces. In this embodiment, desiredappropriate dampening forces can be produced by spring forces from thesprings 54 and a dampening action of the dashpots 55 which have a highdampening efficiency, thereby achieving a real passive stable axis(Y-axis). Specifically, while the electromagnet 4 is limited in itsdegree of translation freedom in the Y-axis direction by the springs 54and the dashpots 55, the Y-axis can be made a good passive stable axisby suitably adjusting the springs 54 and the dashpots 55 which arerestricting elements.

With the passive damper being disposed in the vicinity of a stop pointin the conveyor passage, vibrations of the carriage which are producedin the vicinity of the stop point can quickly be absorbed and dampened.

(10th embodiment)

A vibration dampening mechanism (damper) using magnets in a tunnelaccording to a tenth embodiment of the present invention will bedescribed below with reference to FIGS. 35 and 36.

FIG. 35 is a sectional front elevational view of a magnetic levitationconveyor apparatus according to this embodiment, and FIG. 36 is a planview of the magnetic levitation conveyor apparatus. A basic structure ofthe magnetic levitation conveyor apparatus has been described in detailwith respect to the third embodiment. Like or corresponding parts aredenoted by like or corresponding reference numerals, and will not bedescribed in detail below.

A pair of permanent magnets 56 as first magnets is attached respectivelyto opposite sides of an outer shell 19 of the carriage 3 in the Ydirection. The first permanent magnets 56 are fixedly mounted inrespective recesses 57 defined in the sides of the carriage. Thecarriage 3 has a rectangular opening 0 for taking a wafer 22 into andout of the carriage 3.

Permanent magnets 58 as second magnets are attached respectively toopposite side walls 15 of the partition 2 for producing magnetic forcesbetween themselves and the first permanent magnets 56 and applyingdampening forces against vibrations of the carriage 3. The opposite sidewalls 15 have bottomed grooves 59 defined therein which open outwardly(toward the atmospheric side) and are aligned with the first permanentmagnets 56. The second permanent magnets 58 are fitted respectively inthe grooves 59 for back-and-forth movement in the Y direction. Thegrooves 59 have respective openings covered with lids 60 and fullyclosed by seals. The lids 60 are removably mounted on the side walls 15.

Springs 61 for producing spring forces in the Y direction are interposedbetween the lids 60 and the second permanent magnets 58 for normallybiasing the second permanent magnets 58 toward inner surfaces of theside walls 15. Inner spaces of the grooves 59 in which the springs 61are disposed are filled with oil 62 as a means for producing a dampeningaction. Such an arrangement including the second permanent magnets 58serves to apply dampening forces against vibrations of the carriage 3.For producing a dampening action, resilient members such as of rubbermay be employed in place of the oil 62. In such a modification, thesprings 61 are interposed through the resilient members between the lids60 and the second permanent magnets 58.

In this embodiment, the first and second permanent magnets 56, 58 havesuch magnetic poles which are repelled from each other.

In the magnetic levitation conveyor apparatus of the above arrangement,the carriage 3 is lifted in the tunnel 1 surrounded by the partition 2by the electromagnets 4, and propelled and moved forward by the linearmotors 6. At a stop position S, the carriage 3 is stopped by theelectromagnetic brake 18, and a wafer 22 is taken into and out of thecarriage 3 through the opening O using a robot arm or the like (notshown).

While the carriage 3 is moving in the tunnel 1, the carriage 3 ispositioned in the Y direction by being pulled at all times toward thecentral position in the Y direction because the magnetic member 20 andthe magnetic pole surfaces of the electromagnets 4 have equal widths.When the carriage 3 is in the central position in the Y direction,repulsive forces acting between the first permanent magnets 56 on thecarriage 3 and the second permanent magnets 58 on the partition 2balance each other, allowing the carriage 3 to move while kept in thecentral position. If the carriage 3 is displaced off the centralposition due to centrifugal forces acting thereon or vibrations producedthereon, then the carriage 3 is always pushed back to the centralposition in the Y direction by repulsive forces acting between thepermanent magnets 56, 58. Therefore, the carriage 3 is prevented fromcontacting the inner surfaces of the partition 2. Since the secondpermanent magnets 58 on which magnetic forces from the first permanentmagnets 56 act are attached to the tunnel partition through the springsand the dampening means, when the carriage 3 vibrates, the repulsiveforces are varied and a resultant motion is transmitted to the permanentmagnets 58. As the motion is dampened, the vibrational energy isabsorbed, and the vibrations of the carriage 3 are dampened.Accordingly, even when the carriage 3 starts being vibrated, itsvibrations are quickly dampened.

The first and second permanent magnets 56, 58 may compriseelectromagnets rather than permanent magnets.

(11th embodiment)

A conveyor mechanism with a vertical tunnel according to an eleventhembodiment will be described below with reference to FIGS. 37 and 38.

In FIG. 37, a first conveyor passage la in which a carriage 3 moves isseparated in space by a partition 2 which defines therein a highlypurified space such as of a high vacuum or the like that serves as atunnel.

The carriage 3 is lifted out of contact with the partition 2 undermagnetic attractive forces generated by levitation electromagnets 4disposed outside of the partition 2. The levitation electromagnets 4magnetically attract and lift the carriage 3 which has a magneticmember. Linear motors 6 which comprise electromagnets generate an eddycurrent in an electrically conductive member mounted on a lower surfaceof the carriage 3 to propel the carriage 3 horizontally for thereby movethe carriage 3 horizontally out of contact with the partition 2.

A second conveyor passage 1b differs in height from the first conveyorpassage 1a, but is structurally similar thereto in that the carriage 3in the tunnel is lifted by electromagnets 4 and moved horizontally bylinear motors 6. The magnetic levitation conveyor apparatus includes aconveyor passage 65 as a vertical tunnel which connects the firstconveyor passage la and the second conveyor passage 1b that havedifferent heights.

The vertical conveyor passage 65 comprises a table 66 having alevitation mechanism and a linear motor for magnetically levitating thecarriage 3 out of contact with the tunnel, and an elevator mechanism 67for vertically moving the table 66. The elevator mechanism 67 verticallymoves a shaft 69 with respect to a fixed side 68 while keeping a vacuumcondition in the vertical conveyor passage 65 which is separated inspace by a partition.

The carriage 3 which has been lifted in the first conveyor passage la bythe levitation electromagnets 4 and moved therein by the linear motors 6enters the vertical conveyor passage 65. The linear motor of the table66 produces braking forces to stop the carriage 3 on the table 66 of thevertical conveyor passage 65. The carriage 3 is supported by the table 6out of contact with the table 66 by levitation electromagnets. The table66 is then lowered by the elevator mechanism 67. When the table 66reaches a position horizontally aligned with the second conveyor passage1b, a sensor 8 detects the position of the carriage, and stops themovement of the elevator mechanism 67. At this time, the carriage 3 isat the same height as the second conveyor passage 1b. In this manner,the carriage 3 can move between conveyor passages of different heights,e.g., from the first conveyor passage 1a to the second conveyor passage1b or from the second conveyor passage 1b to the first conveyor passage1a, while being held out of contact with the tunnel partition. Thevertical conveyor passage 65 also defines a highly purified space suchas of a high vacuum separated in space by the partition 2 which is ofthe same material as that of the conveyor passages 1a, 1b.

FIG. 38 shows a detailed structure of the table 66 and the carriage 3.The table 66 has levitation electromagnets 4 and a propulsionelectromagnet 18. The carriage 3 serves to support and convey asemiconductor wafer 22, for example. To an upper surface of the carriage3, there are fixed a magnetic member 20, which is a target of thelevitation electromagnets 4, is fixed to an upper surface of thecarriage 3, and a magnetic member 70, which is a target of thepropulsion electromagnet 18.

When an electric current flows through excitation coils of thelevitation electromagnets 4, the levitation electromagnets 4 generatemagnetic attractive forces to attract the magnetic member 20 to lift thecarriage 3 out of contact with the partition. The propulsionelectromagnet 18 produces horizontal magnetic attractive forces to brakeand stop horizontally the carriage 3 which has entered directly belowthe table 66. To move the carriage 3 into another conveyor passage, thepropulsion electromagnet 18 can generate horizontal propulsive forces topropel the carriage 3 into the other conveyor passage. Sensors 8disposed between magnetic poles of each of the levitation electromagnets4 serve to detect the levitated position of the carriage 3. Based on thedetected positional data of the carriage 3, the electric current flowingthrough the coils of the levitation electromagnets 4 is controlled tokeep the carriage 3 in a suitable levitated position.

These electromagnets 4, 18 and sensors 8 are covered with a can 71, sothat the high-vacuum space in the partition 2 will be prevented frombeing contaminated by any contaminants produced from theseelectromagnets and sensors.

In the above description, the workpiece to be conveyed is asemiconductor wafer. However, the present embodiment is also applicableto a wide variety of apparatus for conveying a workpiece in a tunnelwhile keeping the workpiece lifted out of contact with the tunnel, suchas for conveying a liquid crystal substrate in the production of liquidcrystal displays or the like. The highly purified environment is notlimited to a vacuum condition, but may be a highly pure inert gasatmosphere or the like.

As described above, the conveyor apparatus according to this embodimenthas a plurality of conveyor passages as tunnels which have differentvertical heights and a vertical conveyor passage as a tunnel whichinterconnects the above conveyor passages. Therefore, the conveyorapparatus can move a workpiece between the conveyor passages which havedifferent vertical heights while keeping the workpiece lifted out ofcontact with the partitions. Since the carriage can be moved verticallyin the tunnel surrounded by the partition, the magnetic levitationconveyor apparatus can find an increased range of applications.

(12th embodiment)

A joint chamber for loading a conveyed workpiece into a processingdevice according to a twelfth embodiment of the present invention willbe described below with reference to FIGS. 39 through 41.

FIG. 41 shows a conventional arrangement for loading a conveyedworkpiece into a processing device. A tunnel 1 is a conveyor passage ofa magnetic levitation conveyor apparatus in which a carriage 3supporting a workpiece such as a semiconductor wafer, a liquid crystalsubstrate, or the like moves while lifted out of contact with apartition of a closed space. The tunnel 1 defines therein a highlypurified space which may be of a vacuum or filled with a highly pure N₂gas or the like. Although not shown, there are disposed, outside of thepartition of the tunnel 1, electromagnets having magnetic poles formagnetically levitating the carriage in the closed space, displacementsensors for measuring the gap between the partition surface of theclosed space and the carriage, control circuits for controlling excitingcurrents supplied to the electromagnets based on signals from thesensors, accelerating/decelerating linear motors for moving thecarriage, and a stop device for stopping the moving carriage.

In order that a conveyed workpiece such as a semiconductor wafer fromthe tunnel 1 can be loaded into processing chambers 74 for processingthe workpiece by way of evaporation, photolithography, or the like, achamber 72 is provided which serves as a buffer for keeping theworkpiece clean between the tunnel 1 and the processing chamber 74.

If a substrate 22 such as a wafer is transferred between the carriage 3and one of the processing chambers 74 with a robot 73 in an antechamber77, then the robot 73 is required to have a long reach, and hence itsrobot hand suffers a rigidity problem. To avoid the above drawback,another handling robot 75 is disposed in the chamber 72 for transferringthe substrate 22 from the carriage 3 in the closed space onto a supportbase 76, and the robot 73 in the antechamber 77 draws the substrate 22from the support base 76 and transfers the substrate 22 into one of theprocessing chambers 74.

As described above, if the robot 73 in the antechamber 77 directlytransfers the wafer from the carriage 3 in the closed space into one ofthe processing chambers 74, then the robot hand of the robot 73 isrequired to have a long reach, and hence suffers a rigidity problem. Thehandling robot 75 additionally disposed in the chamber 72 fortransferring the substrate 22 into one of the processing chambers 74through a two-step process is expensive and requires complex controls.Since the substrate 22 is transferred twice by the robot 75 in thechamber 72 and the robot 73 in the antechamber 77, the substrate 22tends to be contaminated with more particles as the number of times thatthe substrate 22 is handled by the robots is increased.

FIG. 39 illustrates an embodiment in which a joint chamber is employed.

A joint chamber 78 connected to a tunnel 1 is disposed between thetunnel 1 and an antechamber 77, and is associated with a partition valve79 on a tunnel 1 side and a partition valve 80 on an antechamber 77side. The joint chamber 78 has a vacuum pump or a source of a highlypure inert gas. Therefore, a highly purified space of the sameatmosphere as the tunnel 1 and processing chambers 74 can be created inthe joint chamber 78. Outside of the joint chamber 78, there aredisposed electromagnets having magnetic poles for magneticallylevitating the carriage in the closed space, displacement sensors formeasuring the gap between the partition surface of the joint chamber andthe carriage, control circuits for controlling exciting currentssupplied to the levitation electromagnets based on signals from thesensors, electromagnets serving as accelerating/decelerating linearmotors for moving the carriage, and an electromagnet serving as a stopdevice for stopping the carriage.

The joint chamber 78 operates as follows: With the valves 79, 80 closed,the joint chamber 78 is evacuated by the vacuum pump. When the degree ofvacuum in the joint chamber 78 becomes equal to that in the tunnel 1,the valve 79 is opened to produce the same atmosphere in the jointchamber 78 as in the tunnel 1. The carriage 3 which supports a substrate22 moves in the tunnel 1, and is stopped in front of the joint chamber78 by the stop device. When the carriage 3 is accelerated toward thejoint chamber 78 by the linear motors, the carriage 3 enters the jointchamber 78 while being magnetically levitated. The carriage 3 is thenstopped in the joint chamber 78 by the stop device in the joint chamber78.

Then, the valve 79 is closed and the valve 80 is opened to equalize theatmosphere in the joint chamber 78 to the atmosphere in the antechamber77. A valve 81 in one of the processing chambers 74 is opened, and thesubstrate 22 is pulled from the carriage 3 by a robot 73 in theantechamber 77 and transferred into the processing chamber 74.Conversely, a substrate 22 can similarly be taken from the processingchamber 74 by the robot 73, and transferred to the carriage 3.

FIG. 40 shows a joint chamber according to another arrangement. In thisarrangement, antechambers 77 are connected to a tunnel 1 in threedirections. As shown in FIG. 40, the tunnel 1 has an end 82 connected tothe antechambers 77 in three directions through respective three jointchamber 78. Each of the joint chambers 78 has levitation electromagnetsand linear motors for magnetically levitating and moving a carriage 3.In each of the joint chambers 78, the carriage 3 can be moved andstopped while being held out of contact with the wall thereof. Thecarriage 3 which has been moved through the tunnel 1 that serves as aconveyor passage is stopped at the end 82, and moved into one of thejoint chambers 78 directly connected to the closed space in the tunnel 1while being held out of contact with the wall thereof. In the jointchamber 78, a workpiece 22 such as a wafer can be transferred betweenthe carriage 3 and a corresponding processing chamber 74 by a robot 73in the antechamber 77. The workpiece 22 can also be transferred betweenthe processing chambers 74 through the three joint chambers 78 via aroute composed of one of the joint chambers 78, the end 82, and anotherof the joint chambers 78, rather than via the tunnel 1.

As described above, the conveyor apparatus according to this embodimenthas the joint chamber for loading a workpiece directly into theprocessing device, and the joint chamber has the means for levitatingthe carriage and moving and stopping the carriage while held out ofcontact with the partition. Accordingly, the wafer can be transferred toand from the processing chamber with a single robot in the antechamber.The substrate can thus be loaded directly into the processing devicewhile being kept in the same purified atmosphere as in the tunnel,without requiring an increased number of handling robots and sufferingthe problem of particle contamination.

Industrial applicability

As described above, the magnetic levitation conveyor apparatus accordingto the present invention can move a carriage in a tunnel defined by apartition while stably levitating the carriage out of contact with thepartition. Therefore, the magnetic levitation conveyor apparatus canconvey a workpiece on the carriage in a highly purified space such as ofa vacuum or a nitrogen gas atmosphere through a conveyor passageincluding an orthogonal branch, without being contaminated by dirt anddust particles which would otherwise be produced by contact with thepartition. The magnetic levitation conveyor apparatus is suitable foruse in semiconductor or liquid crystal substrate fabrication factorieswhich require workpieces to be conveyed in magnetic levitation conveyorapparatus in a highly purified space and have a number of variousprocessing devices.

We claim:
 1. A magnetic levitation conveyor apparatus, comprising:atunnel defined by a partition; a carriage movable in a levitated statethrough said tunnel for conveying a workpiece; levitation electromagnetshaving at least two rows of magnetic poles disposed on an upper portionof said partition of said tunnel for lifting the carriage out of contactwith the partition; electromagnets serving as linear motors and havingat least one row of magnetic poles disposed on a lower portion of saidpartition of said tunnel for moving said carriage out of contact withthe partition; at least two rows of displacement sensors disposed onsaid partition for detecting a levitated portion of said carriage; andcontrol circuits for controlling exciting currents supplied to saidlevitation electromagnets based on output signals from said displacementsensors, said carriage having, on an upper surface thereof, two parallelmagnetic elements corresponding to said two rows of magnetic poles ofthe levitation electromagnets, and also having, on a lower surfacethereof, an electrically conductive member corresponding to the magneticpoles of the electromagnets serving as the linear motors.
 2. A magneticlevitation conveyor apparatus according to claim 1, wherein saidlevitation electromagnets, said linear motors, and said displacementsensors are disposed outside of said partition, and housed in respectivethin-wall casings extending through said partition and partly exposed insaid tunnel.
 3. A magnetic levitation conveyor apparatus according toclaim 1, wherein said partition includes at least upper and lowerpartitions, each of said upper and lower partitions comprises an innershielding thin plate and an outer thick reinforcing plate which is rigidenough to reinforce said thin plate, said levitation electromagnets andsaid linear motors being disposed outside of said tunnel and extendingthrough said reinforcing plate so as to be positioned adjacent to saidthin plate.
 4. A magnetic levitation conveyor apparatus according toclaim 1, wherein said tunnel has substantially orthogonal branchedpassages having at least two rows of levitation electromagnets, andwherein said carriage has two parallel magnetic elements perpendicularto said magnetic elements thereof corresponding to said two rows oflevitation electromagnets.
 5. A magnetic levitation conveyor apparatusaccording to claim 1, wherein said tunnel maintains a vacuum therein. 6.A magnetic levitation conveyor apparatus according to claim 1, whereinsaid tunnel maintains a nitrogen gas atmosphere therein.
 7. A magneticlevitation conveyor apparatus according to claim 1, wherein the twoparallel magnetic elements and the two parallel magnetic elementsperpendicular thereto on the upper surface of said carriage jointlyserve as a magnetic member having a shape of a substantially centrallyopen rectangle.
 8. A magnetic levitation conveyor apparatus according toclaim 7, wherein each of said levitation electromagnets has across-sectionally C-shaped magnetic pole, said magnetic member hassurfaces each having grooves defined therein and extending in adirection in which said carriage is movable and in a directionperpendicular thereto, said grooves corresponding to magnetic polesurfaces of the cross-sectionally C-shaped magnetic pole of each of saidlevitation electromagnets.
 9. A magnetic levitation conveyor apparatusaccording to claim 7, wherein each of said levitation electromagnets hasa cross-sectionally C-shaped magnetic pole, said magnetic member hascomers spaced from sides thereof by gaps in a direction in which saidcarriage is movable and in a direction perpendicular thereto, providingridges corresponding to magnetic pole surfaces of the cross-sectionallyC-shaped magnetic pole of each of said levitation electromagnets.
 10. Amagnetic levitation conveyor apparatus according to claim 1, whereinsaid levitation electromagnets include levitation electromagnets arrayedalong a main conveyor passage and levitation electromagnets arrayedalong a branched conveyor passage, said levitation electromagnetsarrayed along the main and branched conveyor passages being disposedadjacent to each other in a branched point of the tunnel havingsubstantially orthogonal branched passages, further including switchingmeans for switching the levitation electromagnets in an operativecondition into an inoperative condition and the levitationelectromagnets in an inoperative condition in a different conveyingdirection into an operative condition for thereby changing the directionof movement of said carriage between said main and branched conveyorpassages.
 11. A magnetic levitation conveyor apparatus according toclaim 1, further comprising a group of switches for supplying andcutting off currents to said levitation electromagnets to controlswitching of the levitation electromagnets as said carriage moves, aselective signal generator for outputting a signal to select levitationelectromagnets and displacement sensors which are to be turned on andoff, and open and close those of said switches which are associated withthe selected levitation electromagnets and displacement sensors, a gainsetting unit for setting gains of the control circuits, a targetlevitation voltage setting unit for setting a target levitation voltagewhich is a target levitation value, and means for simultaneouslygradually varying the gains of the control circuits or the targetlevitation voltages as target levitation values through said gainsetting unit and/or said target levitation voltage setting unit, withrespect to at least one levitation electromagnet to be turned off whichare selected by said selective signal generator, when the levitationelectromagnets are switched by the control circuits as the carriage ismoved by said linear motors.
 12. A magnetic levitation conveyorapparatus according to claim 1, further comprising a target levitationvoltage setting unit for setting a target levitated position of saidcarriage, and/or a gain setting unit for setting gains of the controlcircuits, said target levitation voltage setting unit and/or said gainsetting unit including digital-to-analog converting means and digitalprocessing means, said digital processing means having a modifiableprocessing program for lessening shocks produced when said carriage islifted and landed.
 13. A magnetic levitation conveyor apparatusaccording to claim 1, further comprising a support device for supportingeach of said levitation electromagnets held in a predetermined positionwith respect to directions in which said carriage is lifted and moved,and supporting each of said levitation electromagnets movably in lateraldirections perpendicular to the direction in which said carriage ismoved, said support device having dampening force applying meansincluding springs and dashpots disposed between each of said levitationelectromagnets and fixed walls of said tunnel.
 14. A magnetic levitationconveyor apparatus according to claim 1, further comprising firstmagnets attached to respective opposite sides of said carriage, andsecond magnets attached to respective opposite side walls of saidpartition for producing magnetic forces between themselves and saidfirst magnets, said second magnets being associated with dampeningmeans.
 15. A magnetic levitation conveyor apparatus according to claim1, further comprising a plurality of tunnels having different heights, avertical tunnel interconnecting said tunnels, said vertical tunnelincluding a table having levitation electromagnets and linear motors formagnetically lifting said carriage, and an elevator mechanism forvertically moving said table.
 16. A magnetic levitation conveyorapparatus according to claim 1, further comprising a joint chamberconnected to said tunnel for loading the workpiece directly into aprocessing device, electromagnets disposed outside of said joint chamberfor magnetically lifting said carriage, electromagnets disposed outsideof said joint chamber and serving as linear motors for moving saidcarriage, and electromagnet disposed outside of said joint chamber forstopping said carriage, and partition valves disposed at respectivefront and rear ends of said joint chamber.